The invention relates generally to miniature motors used in, for example, toys; audio and video equipment, and automotive electrical appliances, hand tools and other motor-driven devices. More particularly, the invention relates to an end cover plate and brush base for a motor casing of a miniature motor.
FIG. 1 is a miniature motor 10 having a metallic cylindrical housing 12. The housing 12 may be formed of mild steel and have a hollow tubular section 14 and an integral bottom 16. The opposite end 30 of the housing is open to receive a brush base and cover plate at one end of the tubular section. Within the housing are fixed a pair of opposite permanent magnets 18, each of which have an arc shape to match the inner wall of the housing. The magnets form between them a volume in the housing for a rotor 20. The rotor includes a cylindrical armature 22 coaxially mounted on a rotor shaft 24. The rotor shaft 24 extends through the opposite ends of the housing 12.
Bearings 26 are mounted to rotatably support the shaft in the ends of the housing. The bottom 16 of the motor housing has an integral flange 28, into which is press-fitted a bearing 26 to support one end of the rotor shaft 24. The opposite end 30 of the housing has an open cylindrical base which receives a brush base 32 and cover plate 34 which are assembled together to fit in the open end 30 of the housing.
The cover plate 34 fits over the base, and the cover plate and brush base fit into the motor housing. The open edge of the housing is crimped onto the plate. The cover plate 34 has a flange 36 to support a bearing 26 which supports an end of the rotor shaft 24. The flange 36 and bearing 26 of the cover plate 34 (when inserted in the motor housing) are coaxially aligned with the flange 28 and bearing 26 on the bottom section 16 of the motor housing so that the rotor shaft is held in coaxial alignment with the motor housing 12.
The brush base 32 supports a pair of brush arms 38 which provide an electrical connection between an external electrical contact 40 of the motor and the armature 22 of the rotor 20. The brush arms are generally strips of copper having a first end fixed to the periphery of the brush base 32 and an opposite, free end on which is mounted a brush 42. The brush arms are attached to opposite sides of the brush base. The brushes on the arms face each other at the axis of the motor. When inserted in the housing, the brushes are in slidable contact with the commutator 44 on the rotor shaft 24. The commutator provides an electrical contact between the wiring of the armature 22 and the brushes.
The external contacts 40 of the brush arms provide direct electrical current (D.C.) through the brushes and the commutator to the windings in the armature 22. Electrical current flowing through the armature creates an alternating magnetic field within the housing that interacts with the magnetic field of the permanent magnets 18. This interaction of magnetic fields creates a force that rotates the rotor 20. This rotation drives the rotor shaft 24 to provide a mechanical rotational output power source from the rotor. The rotor shaft 24 extends through the bottom 16 of the housing to provide a mechanical power output to drive a gear box or other device.
Conventional cover plates 34 are cylindrical discs having embedded recesses which fit into matching slots in the brush base 32 and/or grooves in the end 30 of the housing. Forming a motor plate having recesses, brush bases having slots and machining the motor housing to have the grooves needed to match the cover plate and/or base adds to the complexity and cost of miniature motors. Miniature motors tend to be a relatively-low cost component of toys and other equipment. Accordingly, it is important that manufacturing costs for making these motors be minimized.
The invention is intended to overcome the problems inherent with prior miniature motors having complicated brush bases, and motor plates. Specifically, the invention relates to a simplified construction of a motor housing, brush base and motor plate.
The simplified construction features include a motor housing having an outer end which has a smooth circular edge, that does not require the cutting of slots into the edge. Minimal machining may be applied to the edge to polish an outer ring of the housing and to machine a lip to engage the brush base. The brush base also has a simplified construction and formed by injection molded plastic. Moreover, the brush base has several features which facilitate the assembly of the motor housing including a collar and flange that fit easily into the motor housing to fix the position of the brush base inside the housing. The cover plate, which may be a simple metal stamp construction, fits directly onto a planar region of the brush base.